1. Field of Invention
The present invention relates to an electro-optical device enabling a high-quality gray scale display with low power consumption, a gray scale display method therefor, and an electronic apparatus incorporating the electro-optical device.
2. Description of Related Art
Generally, electro-optical devices produce a display by using electro-optical changes of an electro-optical material. A liquid-crystal device using a liquid crystal as an electro-optical material, which is an example of such an electro-optical device, is constructed as described below. The liquid-crystal device includes a component substrate on which pixel electrodes arranged in a matrix, and switching elements connected to these pixel electrodes are provided, an opposing substrate on which opposing electrodes which oppose pixel electrodes are formed, and a liquid crystal as an electro-optical material, which is held between these two substrates.
In such a construction, when the switching element is placed in a conducting state and a voltage signal corresponding to the gray shade is applied to the pixel electrode, a charge corresponding to the voltage signal is stored in the liquid-crystal capacitor in which a liquid crystal is held by the pixel electrode and the opposing electrode. After the charge is stored, even if the switching element is turned off, the storage of the charge in the liquid-crystal capacitor is maintained by the liquid-crystal capacitor itself, etc. In this manner, when each switching element is driven and the amount of charge to be stored is controlled according to the gray shade, since the orientation state of the liquid crystal is changed, the density is changed for each pixel, making a predetermined gray scale display possible.
However, since the voltage signal to be applied to the pixel electrode is a voltage that corresponds to the gray shade, that is, an analog signal, drawbacks exist, such as the fact that display variations are likely to occur due to nonuniformity of various element characteristics, wiring resistance, etc.
Therefore, in order to eliminate such drawbacks, in recent years, a technology has been proposed, in which one field (frame) is divided according to the bits of the gray scale data, the period of each subfield is set according to the weight of each bit, an ON voltage or an OFF voltage is applied, for each subfield, to the pixel electrode in accordance with the bit corresponding to the subfield. Thus, when one field is viewed as one cycle, the effective value of the voltage applied to the liquid-crystal capacitor is controlled to a value that corresponds to the application of the ON voltage or the OFF voltage in each subfield in order to produce a gray scale display. According to such a method, since a signal to be supplied to the wiring only needs to be a binary signal which indicates either ON or OFF of the pixel, problems arising from the nonuniformity of various element characteristics, wiring resistance, etc., can be eliminated or at least reduced.
However, in such a method, a signal indicating ON or OFF of the pixel must be supplied for each subfield in which one field is divided into a plurality of fields. That is, it is necessary to supply a signal indicating ON or OFF of the pixel at a frequency higher than that of the construction in which one field is not divided into subfields, thereby presenting the problem that power consumption is increased.